Epoxy resins are monomers or prepolymers that react with curing agents to yield high-performance resins. These resins have gained wide acceptance as protective coatings, electrical insulation, structural adhesives, and in structural applications as a matrix resin for composites because they possess a combination of characteristics such as thermal and chemical resistance, adhesion, and abrasion resistance.
Epoxy resins are characterized by the presence of a 3-member cyclic ether group commonly referred to as an epoxy, 1,2-epoxide or an oxirane group. The epoxy resins are cured, or caused to harden, by the addition of a curing or hardening agent. Curing agents used include anhydrides, amines, polyamides, Lewis acids, salts and others. The most common class of epoxy resins are diglycidyl ethers that can be cured by the use of polyamino compounds.
Epoxy resins are frequently required to have high glass transition temperatures in order to have structural properties at high temperatures. A method of achieving high glass transition temperatures in epoxy resins is to prepare resins having high crosslink density and a high concentration of polar groups. This technique is disclosed in U.S. Pat. No. 4,331,582, wherein it is taught that bis[4-(N-N-diglycidylamino)-phenyl]methane (TGDDM) is cured with di(4-aminophenyl)sulfone (DDS). While this method does produce resins that have high glass transition temperatures, the resins have several shortcomings. The materials are very brittle and suffer a large loss in glass transition temperature when exposed to moisture. These problems are caused by the high crosslink density and high concentration of polar groups respectively. DDS can also be used to cure other epoxy resins such as glycidyl ethers of polyhydric phenols. Again, while these resins may be characterized by high glass transition temperatures, they also tend to be very brittle.
Epoxy resin compositions in which the epoxy group-containing compound contains a polycyclic structure and which can be cured to resins having a high glass transition temperature are known. Examples of such resin compositions among others are the glycidyl ethers of polyhydroxy-phenylchroman disclosed in U.S. Pat. No. 2,902,471 and the bisglycidyl ethers of polycarbocyclic substituted bisphenols, e.g., (2-norcamphanylidene)diphenol, described in U.S. Pat. No. 3,298,998; the bisglycidyl ethers of cyclopentenyl substituted bisphenols disclosed in U.S. Pat. No. 3,332,908; and the glycidyl ethers of 9,9-bis(4-hydroxyphenyl)fluorene described in assignee's copending patent application U.S. Ser. No. 830,552, filed Feb. 18, 1986. Although these compositions can be cured using conventional curing agents to resins having a high glass transition temperature, compared to the cured resins of the instant invention, they have a low stiffness as expressed by modulus of elasticity. As is known in the art the chemical structure and ring numbering system of the fluorene compound is as follows: ##STR1##